Functions of the symbols at the top of the screen:
Symbols for emails
Compose an email (see Compose an email)
Print the mail that is currently displayed in the preview pane
Delete all mails that are marked in the maillist (how to mark, see Maillist) Mails are first moved to the trash, deleting them in the trash removes them from the system
Reply to the mail shown in the preview pane (The text of the mail gets included to the new mail, not the attachments)
Perform an (inline) forward of the mail (The text of the mail is attached to the new mail, not the attached files)
Completely forward the mail (The whole mail is included as one attachment to the new mail)
Receive new messages (This requires an account to be set up, see Email Accounts)
Open the tab for settings (see Email Accounts, General Settings)